GNU LilyPond 2.19.83
Preprocessing graphical objects...
Finding the ideal number of pages...
Fitting music on 1
failed assertion `ret <= cached_line_details_.size ()'
Note, oddly, that almost every line in the MWE above needs to be present to
trigger the core. That is: commenting out \autoPageBreaksOff prevents the
core; reducing the example from four staves to three staves prevents the
core; selecting a different series of time signatures for the example
prevents the core (?!); even commenting out the TimeSignature.font-size
override prevents the core (?!).